There's now a more recent interview about Hayabusa where Team Ninja is once again saying he's waiting for an invitation. Since they don't actually own the series, I don't take what they say as a deconfirmation.
But anyway, I've been wondering, does anybody else think the Ralf & Clark spirit battle could possibly be like a low-key reference to Contra? I know out of all the characters in the roster, Snake makes the most sense for obvious reasons but I do think about how Snake is from the same company that just happens to have their own run-and-gun series just like Ikari Warriors. It just makes the spirit battle all the more fitting.